1. Field of the Invention
The present invention relates to a disk drive device having a hub on which a recording disk is mounted.
2. Description of the Related Art
Recently, a disk drive device such as an HDD has been improved in bearing stiffness by incorporating a dynamic pressure fluid bearing unit. There is a case that such a disk drive device having the dynamic pressure fluid bearing unit is mounted on a small portable apparatus. A portable apparatus is desired to be further thinned and lightened. Therefore, the disk drive device which is mounted on the portable apparatus is desired to be further thinned and lightened.
For example, patent document 1 has disclosed a disk drive device having a dynamic pressure fluid bearing unit with a first radial dynamic pressure groove of which the formed width in the axial direction is narrower than that of a second radial dynamic pressure groove.    Patent document 1: Japanese Patent Application Laid-Open No. 2007-198555
In order to thin a disk drive device, it is necessary to thin a spindle drive unit and dynamic pressure fluid bearing unit of the disk drive device. Here, when the spindle drive unit is further thinned, there may be a case that the rotation becomes unstable due to a decrease in torque. Further, when the dynamic pressure fluid bearing unit is further thinned, there may be a case that rotation of the disk becomes unstable due to a decrease in the stiffness of the dynamic pressure fluid bearing unit. When the rotation becomes unstable as mentioned above, there may be a case, at the very worst, where the normal reading/writing operation of magnetic data cannot be performed.